1. Field of the Invention
This invention relates to a system for reducing the noise created by internal combustion engines and has particular reference to a system for suppressing the noise created by an aircraft gas turbine engine, and for otherwise enhancing the operation of such engines.
2. Description of the Prior Art
It is statistically known that approximately 95% of the undesirable noise occurring at large airports in the U.S. and foreign countries is due to gas turbine driven, multi-engine aircraft while on the ground or on take-off or on landing.
For many years engine and aircraft manufacturers, along with government agencies, have been actively engaged in attempting to reduce the noise level of such aircraft engines. Generally, the noise is due to the high velocity at which the exhaust gases exit the exhaust nozzle, producing sound waves which radiate in all directions.
This problem has not yet been wholly solved and various municipalities throughout the United States and foreign countries have enacted laws in an attempt to reduce airport noise.
As examples of the prior attempts to reduce engine noise, particularly in aircraft engines, reference may be had to the following U.S. Pat. No. 3,463,402 issued to C. E. Langston, Jr.; U.S. Pat. No. 3,987,621 issued to J. Sabatelli et al; U.S. Pat. No. 4,909,346 issued to D. W. Torkelson; U.S. Pat. No. 4,979,587 issued to W. J. Hirt et al; U.S. Pat. No. 5,154,052 issued to R. G. Griffen et al ; and U.S. Pat. No. 5,216,878 issued to A. W. Klees.
In many of such prior systems, an annular stream of bypass air is passed over the engine and mixed with the exhaust gases before the latter emerge from the exhaust nozzle. This mixing results in a certain amount of noise attenuation due to the turbulence and breaking up of the noise waves before emergence. Although this may reduce the velocity of the exhaust gases with consequent reduction in noise, it also tends to reduce thrust.
In other systems, as noted in the published book "Aircraft Power Plants", fourth edition, by Ralph D. Bent and James L. McKinley, pages 422 and 423, the exhaust gas stream is divided into a number of smaller streams or is so formed to increase the noise frequencies so that they are more highly and quickly attenuated by atmospheric absorption. However such solutions leave much to be desired in reducing exhaust noise to an acceptable level. Also, most such prior attempts to attenuate noise tend to reduce engine power, particularly when most needed, i.e. at take-off, etc.
It therefore becomes a principal object of the present invention to reduce the noise level of engine exhaust gases emitted from an internal combustion engine.
Another object of the invention is to reduce the noise level of the engine without reducing engine power.
Another object is to selectively increase engine power when needed.
Another object is to utilize vortices generated by streams of cooling air to contain and attenuate engine exhaust noises.
A further object is to provide a simple and inexpensive system for reducing the noise level of engine exhaust noises.
Another object is to reduce the noise level and to use the noise energy for added thrust.